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Top 5 Free Currency Converter APIs for Developers in 2026

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If you've ever needed historical exchange rates for backtesting a trading algorithm, or wanted to convert currencies in an app without worrying about API limits, you know the pain of finding a reliable free currency API.

Most free APIs give you current rates. Some give you a few years of history. Almost none give you 57 years.

Here's the rundown of the top free currency converter APIs available in 2025.

1. UniRateAPI — 57 Years of Historical Data

What makes it different: UniRateAPI has exchange rate data going back to 1967. That's the Bretton Woods era. No other free API comes close.

Base URL: https://api.unirateapi.com
Free tier: 2,000 requests/day
Currencies: 593 (including crypto + precious metals)
Historical data: 1967–present
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from unirate import UnirateClient

client = UnirateClient('your_api_key')

# Current rate
rate = client.get_rate('EUR', 'USD')

# Historical rate from 2008
result = client.get_historical_rate('2008-09-15', 100, 'EUR', 'USD')
# Black Monday: €100 = $68.25
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Perfect for: Trading bot backtesting, financial research, historical analysis.

Website: https://unirateapi.com

2. Frankfurter — Open Source, No Account Required

What makes it different: Frankfurter is completely open source and doesn't require an API key. Data comes from the European Central Bank.

Base URL: https://api.frankfurter.app
Free tier: Unlimited (no auth required)
Currencies: ~30
Historical data: 1999–present (4 years)
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// No API key needed
fetch('https://api.frankfurter.app/latest?from=USD&to=EUR')
  .then(r => r.json())
  .then(d => console.log(d.rates.EUR))
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Perfect for: Quick prototypes, small projects, open source projects.

3. ExchangeRate-API — Generous Free Tier

What makes it different: 1,500 requests/month on the free plan with 160+ currencies.

Base URL: https://v6.exchangerate-api.com
Free tier: 1,500 requests/month
Currencies: 160+
Historical data: Not on free tier
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Sign up at https://www.exchangerate-api.com

4. Open Exchange Rates — The Old Standard

What makes it different: One of the original currency API services. 1,000 requests/month free.

Base URL: https://openexchangerates.org/api/
Free tier: 1,000 requests/month
Currencies: 200+
Historical data: Extra cost
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Requires API key. Historical data requires paid plan.

5. CurrencyLayer — Professional Features

What makes it different: Bank-level accuracy and time-zone aware queries.

Base URL: http://api.currencylayer.com
Free tier: 100 requests/month
Currencies: 170+
Historical data: Extra cost
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Which Should You Choose?

API Currencies Historical Free Tier
UniRateAPI 593 57 years 2000/day
Frankfurter ~30 4 years Unlimited
ExchangeRate-API 160+ No 1500/mo
Open Exchange Rates 200+ Extra cost 1000/mo

If you need historical data, UniRateAPI is the only choice that gives you decades of data on the free tier. If you're just doing current conversions and don't want to sign up for an API key, Frankfurter is solid.

For most developer use cases, I'd start with UniRateAPI's free tier — the 2000 requests/day is generous, and the 57-year historical dataset is genuinely unique.testSTART123

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